Charge ordering in Ni$^{1+}$/Ni$^{2+}$ nickelates: La$_4$Ni$_3$O$_8$ and La$_3$Ni$_2$O$_6$

TL;DR

This study uses ab initio calculations to identify charge ordering and insulating behavior in La4Ni3O8 and La3Ni2O6 nickelates, revealing similarities to cuprates and other nickelates.

Contribution

It uncovers the origin of superlattice peaks as charge stripes and predicts checkerboard order in La3Ni2O6, linking these nickelates to known cuprate and nickelate compounds.

Findings

Charge stripes in La4Ni3O8 from Ni2+/Ni1+ ordering.

Insulating state due to structural and magnetic effects.

Predicted checkerboard charge order in La3Ni2O6.

Abstract

Ab initio calculations have been performed to unravel the origin of the recently found superlattice peaks in the trilayer nickelate La$_4$Ni$_3$O$_8$. These peaks arise from static charge ordering of Ni$^{2+}$/ Ni$^{1+}$ stripes oriented at 45$^{\circ}$ to the Ni-O bonds. An insulating state originates from a combination of structural distortions and magnetic order, with the gap being formed solely within the d$_{x^2-y^2}$ manifold of states. When doped, electrons or holes would go into these states, in a similar fashion to what occurs in the cuprates. Analogous calculations suggest that checkerboard charge order should occur in the bilayer nickelate La$_3$Ni$_2$O$_6$. These results reveal a close connection between La$_4$Ni$_3$O$_8$ and La$_3$Ni$_2$O$_6$ with La$_{2-x}$Sr$_x$NiO$_4$ for x=1/3 and x=1/2, respectively.